This paper presents work aimed at supporting the design of temporal aspects of socio-technical systems. Time Design is a framework for (a) analysing and representing temporal properties of the work domain, (b) generating design options that support timely, flexible and dependable function servicing, and (c) providing knowledge about the characte...

This paper presents work aimed at supporting the design of temporal aspects of socio-technical systems. Time Design is a framework for (a) analysing and representing temporal properties of the work domain, (b) generating design options that support timely, flexible and dependable function servicing, and (c) providing knowledge about the characteristics and biases of human temporal control behaviour. In support of the latter end, two microworld experiments that investigated temporal control decisions in a supervisory control task are presented. These experiments manipulated event rate, the duration of event rate blocks, the availability of online and offline event rate information, and the accuracy of this information. The studies identified conditions where attention to temporal information decreased and the use of conservative temporal control strategies increased. Minimize

We address the stability of solitary pulses as well as some other traveling structures near the onset of spatiotemporal chaos in a two-species reaction–diffusion model describing the oxidation of CO on a Pt(1 1 0) surface in one spatial dimension. First, the boundary of the existence region of stable pulses is explored by means of numerical inte...

We address the stability of solitary pulses as well as some other traveling structures near the onset of spatiotemporal chaos in a two-species reaction–diffusion model describing the oxidation of CO on a Pt(1 1 0) surface in one spatial dimension. First, the boundary of the existence region of stable pulses is explored by means of numerical integration of the reaction– diffusion equations. The partial differential equations (PDEs) of the model are next reduced to a set of ordinary differential equations (ODEs) by the introduction of a moving frame and a detailed analysis of traveling wave solutions and their bifurcations is presented. The results are then compared to findings in numerical simulations and stability computations in the full PDE. The solutions of the ODE are organized around a codimension-2 global bifurcation from which two branches of homoclinic orbits corresponding to solitary pulse solutions in the PDE originate. This bifurcation mediates a change in the dynamics of the excitable medium, as seen in numerical simulations, from a regime dominated by stable pulses and wavetrains traveling with constant shape and speed to spatiotemporally chaotic dynamics. We also find a branch of heteroclinic orbits corresponding to fronts in the PDE. Even though these fronts are found to be unstable for the PDE, their spatial signature is frequently observed locally as part of the spatiotemporally chaotic profiles obtained by direct numerical simulation. Minimize

We address the stability of solitary pulses as well as some other travelling structures near the onset of spatiotemporal chaos in a two-species reaction-diffusion model describing the oxidation of CO on a Pt(110) surface in one spatial dimension. First, the boundary of the existence region of stable pulses is explored by means of numerical integ...

We address the stability of solitary pulses as well as some other travelling structures near the onset of spatiotemporal chaos in a two-species reaction-diffusion model describing the oxidation of CO on a Pt(110) surface in one spatial dimension. First, the boundary of the existence region of stable pulses is explored by means of numerical integration of the reaction-diffusion equations. The partial differential equations (PDE) of the model are next reduced to a set of ordinary differential equations (ODE) by the introduction of a moving frame and a detailed analysis of travelling wave solutions and their bifurcations is presented. The results are then compared to findings in numerical simulations and stability computations in the full PDE. The solutions of the ODE are organized around a codimension-2 global bifurcation from which two branches of homoclinic orbits corresponding to solitary pulse solutions in the PDE originate. This bifurcation mediates a change in the dynamics of the e. Minimize

Nanoscale pattern formation in reactive adsorbates on single crystal surfaces is investigated theoretically. Because on such small scales fluctuations become important, a mesoscopic theory for the adsorbate coverage is developed, which aims at providing a link between microscopic lattice models and reaction-diffusion equations. It describes the ...

Nanoscale pattern formation in reactive adsorbates on single crystal surfaces is investigated theoretically. Because on such small scales fluctuations become important, a mesoscopic theory for the adsorbate coverage is developed, which aims at providing a link between microscopic lattice models and reaction-diffusion equations. It describes the dynamics for the locally averaged adsorbate coverages in a continuum model taking into account internal fluctuations. This approach is applied to several systems, where patterns on scales smaller than the characteristic diffusion length, which typically lies in the micrometer range, can be formed. As has been observed e.g. in recent experiments with fast scanning tunneling microscopy, a variety of nanoscale patterns can result from the presence of attractive adsorbate-adsorbate interactions. Here, at first a single species of such an adsorbate is considered. In the absence of nonequilibrium reactions, strong enough attractive lateral interactions can induce a first-order phase transition in the adsorbate coverage. The mesoscopic evolution equation is applied to model the kinetics of this phase transition. If additionally a nonequilibrium reaction is present, stationary spatially periodic microstructures may arise as a result of the competition of the attractive lateral interactions and the reactions. The conditions for their appearance and their properties are investigated in detail, e.g. alternating lateral interactions are discussed and the influence of global coupling through the gas phase is analyzed. Furthermore, it is shown that they are not destroyed by relatively strong internal fluctuations. In the next step, a hypothetical model for two different reactive adsorbate species is investigated, where a similar mechanism leads to the formation of nanoscale traveling and standing waves. In the presence of relatively strong internal fluctuations these waves break up and a complex dynamics of interacting wave fragments is observed. In the last example, it is shown in the analysis of a simple model that self-organized nonequilibrium microreactors with submicrometer sizes may spontaneously develop in a single reactive adsorbate species without attractive lateral interactions. They represent localized structures resulting from the interplay between reaction, diffusion and an adsorbate-induced structural transformation of the surface. Minimize

A new device and method to measure rabbit knee joint angles are described. The method was used to measure rabbit knee joint angles in normal specimens and in knee joints with obvious contractures. The custom-designed and manufactured gripping device has two clamps. The femoral clamp sits on a pinion gear that is driven by a rack attached to a ma...

A new device and method to measure rabbit knee joint angles are described. The method was used to measure rabbit knee joint angles in normal specimens and in knee joints with obvious contractures. The custom-designed and manufactured gripping device has two clamps. The femoral clamp sits on a pinion gear that is driven by a rack attached to a materials testing system. A 100 N load cell in series with the rack gives force feedback. The tibial clamp is attached to a rotatory potentiometer. The system allows the knee joint multiple degrees-of-freedom (DOF). There are two independent DOF (compression-distraction and internal-external rotation) and two coupled motions (medial-lateral translation coupled with varus-valgus rotation; anterior-posterior translation coupled with flexion-extension rotation). Knee joint extension-flexion motion is measured, which is a combination of the materials testing system displacement (converted to degrees of motion) and the potentiometer values (calibrated to degrees). Internal frictional forces were determined to be at maximum 2% of measured loading. Two separate experiments were performed to evaluate rabbit knees. First, normal right and left pairs of knees from four New Zealand White (NZW) rabbits were subjected to cyclic loading. An extension torque of 0.2 Nm was applied to each knee. The average change in knee joint extension from the first to the fifth cycle was 1.9 deg ± 1.5 deg (mean ± sd) with a total of 49 tests of these eight knees. The maximum extension of the four left knees (tested 23 times) was 14.6 deg ± 7.1 deg, and of the four right knees (tested 26 times) was 12.0 deg ± 10.9 deg. There was no significant difference in the maximum extension between normal left and right knees. In the second experiment, nine skeletally mature NZW rabbits had stable fractures of the femoral condyles of the right knee that were immobilized for five, six or 10 weeks. The left knee served as an unoperated control. Loss of knee joint extension (flexion contracture) was demonstrated for the experimental knees using the new methodology where the maximum extension was 35 deg ± 9 deg, compared to the unoperated knee maximum extension of 11 deg ± 7 deg, 10 or 12 weeks after the immobilization was discontinued. The custom gripping device coupled to a materials testing machine will serve as a measurement test for future studies characterizing a rabbit knee model of post-traumatic joint contractures. Minimize

T-type voltage-gated calcium (Ca2+) channels play critical roles in controlling neuronal excitability, firing patterns, and synaptic plasticity, although the mechanisms and extent to which T-type Ca2+ channels are modulated by G-protein coupled receptors (GPCRs) remains largely unexplored. Investigations into T-type modulation within native neuronal systems have been complicated by the presence of multiple GPCR subtypes and a lack of pharmacological tools to separate currents generated by the three T-type isoforms; Cav3.1, Cav3.2, and Cav3.3. We hypothesize that specific Cav3 subtypes play unique roles in neuronal physiology due to their differential functional coupling to specific GPCRs. Co-expression of T-type channel subtypes and GPCRs in a heterologous system allowed us to identify the specific interactions between muscarinic acetylcholine (mAChR) or metabotropic glutamate (mGluR) GPCRs and individual Cav3 isoforms. Perforated patch recordings demonstrated that activation of Galpha<q/11>-coupled GPCRs had a strong inhibitory effect on Cav3.3 T-type Ca2+ currents but either no effect or a stimulating effect on Cav3.1 and Cav3.2 peak current amplitudes. Further study of the inhibition of Cav3.3 channels by a specific Galpha<q/11>-coupled mAChR (M1) revealed that this reversible inhibition was associated with a concomitant increase in inactivation kinetics. Pharmacological and genetic experiments indicated that the M1 receptor-mediated inhibition of Cav3.3 occurs specifically through a Galpha<q/11> signaling pathway that interacts with two distinct regions of the Cav3.3 channel. As hypothesized, the potentiation of Cav3.1 channels by a Galpha<q/11>-coupled mGluR (mGluR1) initially characterized in the heterologous system was also observed in a native neuronal system: the cerebellar Purkinje cell (PC). In recordings on PCs within acute cerebellar slices, we demonstrated that the potentiation of Cav3.1 currents by mGluR1 activation is strongest near the threshold of T-type currents, enhancing the excitability of PCs. Ultrafast two-photon Ca2+ imaging demonstrated that the functional coupling between mGluR1 and T-type transients occurs within dendritic spines, where synaptic integration and plasticity occurs. A subset of these experiments utilized physiological synaptic activation and specific mGluR1 antagonists in wild-type and Cav3.1 knock-out mice to show that the mGluR1-mediated potentiation of Cav3.1 T-type currents may promote synapse-specific Ca2+ signaling in response to bursts of excitatory inputs. Minimize

Estuaries are productive ecological transition zones between freshwater and marine environments that provide important commercial, recreational, aesthetic and cultural resources. The Avon-Heathcote estuary in Christchurch, New Zealand, is no exception, and its close proximity to different kāinga and Christchurch city has provided cultural, recre...

Estuaries are productive ecological transition zones between freshwater and marine environments that provide important commercial, recreational, aesthetic and cultural resources. The Avon-Heathcote estuary in Christchurch, New Zealand, is no exception, and its close proximity to different kāinga and Christchurch city has provided cultural, recreational and aesthetic values for centuries, especially Mahinga kai for Tangata Whenua. Tuangi (The New Zealand cockle, Austrovenus stutchuryi) is an important source of Mahinga kai to the iwi Ngai Tahu, but also an important ecological ecosystem engineer that provides internal habitat to parasites and, through its shell production, external habitat (hard substratum) for epibiota species. Several parasites, in particular the metacercariae echinostome parasite Curtuteria australis, depend on Austrovenus as its intermediate host, and these parasites can be considered allogenic engineers because they turn living material (here the host) from one physical state into a second. This is particularly evident in intertidal sedimentary estuaries where parasites, including Curtuteria, can alter the behaviour and fitness of the ecosystem-engineering hosts and thereby alter entire community structures. Similarly, several epibiota species depend on the shell of Austrovenus as a substratum on which to live. This hard substratum is particularly important for epibiota in estuaries that are devoid of rocky reefs, including autogenic ecosystem engineers like common large macroalgae (e.g. Ulva spp.). However, the Avon-Heathcote estuary, like many estuaries around the world, has become nutrient-enriched following sewage wastewater discharges, input from rivers and encroaching urban development, facilitating enhanced growth of algae attached to shells. Following recruitment and rapid growth on the shells, large algal fronds can break off and accumulate into thick mats that may cause anoxia and detrimental effects on many estuarine organisms. The main objective of this thesis is to quantify key linkages between three types of ecosystem engineers; the cockle Austrovenus, its internal parasites and its external epibiota community, including large macroalgae that can detach from the shell and develop into free-living mats. To address these objectives, spatial-temporal field surveys and laboratory and field experiments investigated (i) when and where Austrovenus provide internal habitat to parasites and external habitat to epibiota, and (ii) if and how parasites and epibiota affect survival and positioning of Austrovenus in or on the sediment. It was hypothesized that parasites and epibiota species would be abundant in and on Austrovenus and that their densities would vary across seasons and environmental gradients. It was also expected that parasites would reduce the ability of Austrovenus to bury themselves, so that surface-lying cockles would have higher parasite densities and be more susceptible to predation. Finally, it was hypothesized that a cover of macroalgae would decrease the susceptibility of Austrovenus to predation, but have negative effects on associated epibiota species, and that herbivorous epibiota species, through grazing, could control the abundance of epibiotic Ulva recruits. Seasonal collections of Austrovenus showed that parasite densities varied in different environments within the estuary (mean ranged from 3-129 for buried hosts and 7-187 for surface-selected hosts). However, host parasite loads did not vary between seasons. Parasite infestation was, found to be slightly higher in hosts exposed above the sediment compared to those buried in sediment. However, the test factor host position accounted for < 1% of the total data variability and therefore host position is of relative low ecological importance. Spatial variability in host parasite loads was significantly correlated to host sizes (its width, Rho = 0.72), individual epibiota species (Anthopleura and Elminius, Rho = –0.11 and Rho = 0.1, respectively), percentage coarse ssediment (Rho = 0.55), and less so to salinity (Rho = 0.42) and elevation level (Rho = 0.33), although the latter two variables were not statistically significant. A laboratory experiment did not confirm the expected hypothesis that hosts with high parasites loads had impaired burrowing ability. A 6-week field experiment, where the burrowing ability of the host was manipulated to increase its visibility, showed that hosts with reduced burrowing abilities did not have higher mortality than hosts with normal burring ability. Epibiota species were also highly variable in the estuary. A spatial survey from 15 sites found four encrusting and 11 solitary epibiota species with highly variable densities across sites and seasons. Factors that accounted for epibiota richness and density included host size and seasonality (particularly for macroalgal species), whereas environmental gradients and co-occurrence patterns with different epibiota species explained additional variability for only a few species. Foliose and tubular forms of Ulva spp. were the most abundant epibiota species throughout estuary (on average 2.3 and 1.7 per host, respectively) and were therefore studied in more detail. A 6-week field experiment showed that drift macroalgal mats had little effect on densities of either Austrovenus or epibiota species. Similarly, another field experiment showed that predators had no impact on Austrovenus abundances, irrespective of its size, if Austrovenus was allowed to bury or not, and if it was unconcealed or concealed under macroalgal mats. Finally, a laboratory experiment showed that small meso-grazers, under natural background densities, could not reduce densities or sizes of Ulva recruits on shells or barnacles (attached to Austrovenus shells). This study has shown that a single species of estuarine shell-forming ecosystem engineer provides ubiquitous internal and external habitat for other species throughout an estuary. The study has helped clarify how ecosystem engineers can directly control species abundances (here of parasites and epibiota) but also function as nursery grounds for other important ecosystem engineers (here bloom-forming drift algae). Furthermore, and in contrast to past research, this study did not find strong relationships between parasites and Austrovenus or its epibiota, suggesting that past generalisations about parasite effects may not be applicable within and between all estuaries. Finally, the study documented that drift macroalgae and consumers, in natural background densities, had very little impact on Austrovenus and its epibiota. Previous studies have shown that hosts with high parasite loads are commonly found on the sediment surface. These studies have suggested that this impaired burial ability makes the host more vulnerable to predation (by the parasites final host). However, at the same time, surface-lying host are also more exposed to fouling by epibiota species, which could reduce predation (by the final host) because epibiota may conceal it. However, this thesis found little support for either of these opposing ecological processes; parasite loads did not decrease burial ability, and host exposed the surface were not predated more, irrespective of being concealed or not Clearly, future studies should aim to identify thresholds in space, time, and densities where parasites, macroalgae and consumers have stronger impacts on Austrovenus and each other than shown here. Minimize

T-type voltage-gated calcium (Ca2+) channels play critical roles in controlling neuronal excitability, firing patterns, and synaptic plasticity, although the mechanisms and extent to which T-type Ca2+ channels are modulated by G-protein coupled receptors (GPCRs) remains largely unexplored. Investigations into T-type modulation within native neuronal systems have been complicated by the presence of multiple GPCR subtypes and a lack of pharmacological tools to separate currents generated by the three T-type isoforms; Cav3.1, Cav3.2, and Cav3.3. We hypothesize that specific Cav3 subtypes play unique roles in neuronal physiology due to their differential functional coupling to specific GPCRs. Co-expression of T-type channel subtypes and GPCRs in a heterologous system allowed us to identify the specific interactions between muscarinic acetylcholine (mAChR) or metabotropic glutamate (mGluR) GPCRs and individual Cav3 isoforms. Perforated patch recordings demonstrated that activation of Galpha<q/11>-coupled GPCRs had a strong inhibitory effect on Cav3.3 T-type Ca2+ currents but either no effect or a stimulating effect on Cav3.1 and Cav3.2 peak current amplitudes. Further study of the inhibition of Cav3.3 channels by a specific Galpha<q/11>-coupled mAChR (M1) revealed that this reversible inhibition was associated with a concomitant increase in inactivation kinetics. Pharmacological and genetic experiments indicated that the M1 receptor-mediated inhibition of Cav3.3 occurs specifically through a Galpha<q/11> signaling pathway that interacts with two distinct regions of the Cav3.3 channel. As hypothesized, the potentiation of Cav3.1 channels by a Galpha<q/11>-coupled mGluR (mGluR1) initially characterized in the heterologous system was also observed in a native neuronal system: the cerebellar Purkinje cell (PC). In recordings on PCs within acute cerebellar slices, we demonstrated that the potentiation of Cav3.1 currents by mGluR1 activation is strongest near the threshold of T-type currents, enhancing the excitability of PCs. Ultrafast two-photon Ca2+ imaging demonstrated that the functional coupling between mGluR1 and T-type transients occurs within dendritic spines, where synaptic integration and plasticity occurs. A subset of these experiments utilized physiological synaptic activation and specific mGluR1 antagonists in wild-type and Cav3.1 knock-out mice to show that the mGluR1-mediated potentiation of Cav3.1 T-type currents may promote synapse-specific Ca2+ signaling in response to bursts of excitatory inputs. Minimize

T-type voltage-gated calcium (Ca2+) channels play critical roles in controlling neuronal excitability, firing patterns, and synaptic plasticity, although the mechanisms and extent to which T-type Ca2+ channels are modulated by G-protein coupled receptors (GPCRs) remains largely unexplored. Investigations into T-type modulation within native neuronal systems have been complicated by the presence of multiple GPCR subtypes and a lack of pharmacological tools to separate currents generated by the three T-type isoforms; Cav3.1, Cav3.2, and Cav3.3. We hypothesize that specific Cav3 subtypes play unique roles in neuronal physiology due to their differential functional coupling to specific GPCRs. Co-expression of T-type channel subtypes and GPCRs in a heterologous system allowed us to identify the specific interactions between muscarinic acetylcholine (mAChR) or metabotropic glutamate (mGluR) GPCRs and individual Cav3 isoforms. Perforated patch recordings demonstrated that activation of Galpha<q/11>-coupled GPCRs had a strong inhibitory effect on Cav3.3 T-type Ca2+ currents but either no effect or a stimulating effect on Cav3.1 and Cav3.2 peak current amplitudes. Further study of the inhibition of Cav3.3 channels by a specific Galpha<q/11>-coupled mAChR (M1) revealed that this reversible inhibition was associated with a concomitant increase in inactivation kinetics. Pharmacological and genetic experiments indicated that the M1 receptor-mediated inhibition of Cav3.3 occurs specifically through a Galpha<q/11> signaling pathway that interacts with two distinct regions of the Cav3.3 channel. As hypothesized, the potentiation of Cav3.1 channels by a Galpha<q/11>-coupled mGluR (mGluR1) initially characterized in the heterologous system was also observed in a native neuronal system: the cerebellar Purkinje cell (PC). In recordings on PCs within acute cerebellar slices, we demonstrated that the potentiation of Cav3.1 currents by mGluR1 activation is strongest near the threshold of T-type currents, enhancing the excitability of PCs. Ultrafast two-photon Ca2+ imaging demonstrated that the functional coupling between mGluR1 and T-type transients occurs within dendritic spines, where synaptic integration and plasticity occurs. A subset of these experiments utilized physiological synaptic activation and specific mGluR1 antagonists in wild-type and Cav3.1 knock-out mice to show that the mGluR1-mediated potentiation of Cav3.1 T-type currents may promote synapse-specific Ca2+ signaling in response to bursts of excitatory inputs. Minimize